Decware Zen Head ZKIT3 Portable Headphone Amp

The competitive portable headphone amplifier market can be a difficult one to approach. Manufactures quickly churn out new designs and form factors so quickly that unless you spend lots of time on HeadFi, it's difficult to keep track of them all. Between Ray Samuels, HeadAmp, HeadRoom, iBasso, Fiio, and many others, there are enough offerings to make your head spin.

The company Decware, known mostly for their non-portable, tube-based amplifiers, released a portable headphone amplifier back in 2008. While it was only four years ago, there have been hundreds, if not thousands, of portable amplifiers released since then that may have made some headphone enthusiasts forget about it. It was reviewed favorably many moons ago by HeadFi member Skylab whose opinion I respect, and Decware is offering the PCBs and chassis on his website, so I figured it would be a nice diversion to put one together and have a listen, even if it is a few years old ;)

The Decware Zen Head PCB

One of the nice things about the Zen Head PCB is that there's no SMD soldering to worry about, which is almost a given with more modern portable designs. Just regular old through-hole components here. This may not be the best beginners project as there isn't really any online documentation other than a bill of materials to populate the board. Also unusually, the parts values are printed directly on the board rather than part designations.

Rather than simply ordering the BoM, I opted to try a few other parts. All the resistors are Takman REX carbon film, and there are quite a few of them as seen below.

Takman carbon film resistors - pretty in pink

The capacitors were switched with Nichicon / Wima equivalents. Also added were a pair of gold sockets so the OPA2132P op-amps could possibly be rolled in the future. All other parts remained identical to the BoM except for items that were out of stock and necessitated a substitute. After the population of all the parts the board is quite colorful!

The populated PCB

The chassis is a little long compared to other portable amps as the battery doesn't fit on or over the board, but in a plastic battery holder in the back. Compared to something like Ray Samuel's Shadow, this amp is massive, but it will still fit in your pocket or transport just fine in a case. A pattern was drilled on the top of the case for heat dissipation, although it's doubtful that much will be generated.

Zen Head in PCB in case

I noted that the PCB was a little long and ran into the battery compartment. Since there's no traces at the end of the board, the PCB was sanded down a bit so everything would fit nicely. The battery strap was then soldered in place.

Attachment of the battery strap

Next the front plate needed to be drilled. A template was printed from the Decware site that was printed at actual size (not fit to page, very important!) and taped to the front of the plate. The plate was then drilled using a drill press and the holes de-burred.

Drilled front plate

More to come!


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The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 

The Objective2 (O2) Headphone Amp

People feel so strongly about audio reproduction that it often becomes akin to religion and politics and arguments ensue. Some listeners feel that a perfectly flat response curve and fully diminished THD levels (total harmonic distortion) are the holy grail, while there are others that enjoy the warm distortion and harmonics achieved with old triode technology and a frequency response that tapers the upper and lower extremes. Both are right in their own way, the former looking for perfect accuracy, the latter looking for a relaxing listening experience, and there are probably many listeners that fall in between.

The Objective2 headphone amp falls into the first category, where good measurements are the paramount objective. NwAvGuy has gone to great lengths to provide what many headphone listeners have been pining for, a low-cost headphone amp that achieves great measurements in a vast number of categories. While I don't fall into the category of pursuing perfect measurements (just look at all the number of tubes used in the builds on this site), I highly respect the effort that went into this build and all subsequent documentation.

Something that's quite impressive is that NwAvGuy does not make a penny from these designs. The PCB files are open source and circulated freely; users are encouraged to arrange group-buys on forums such as DIYAudio.com in order to procure the board and/or the front panel. Also, as of this writing, JDSLabs is offering both the O2 board and a unique front panel (to see the JDSLabs CMoyBB being built, please see my previous post). The total cost of the build is very reasonable and should fall under $100 including the case, custom front panel and wall-wart. Add a couple hours of soldering time and you'll have yourself an amp.

The Objective2 Sept 2011 PCB board

What's especially important with closely populated boards is starting with the small parts (resistors and diodes) and working your way up to the larger items such as capacitors and MOSFETs. If one doesn't follow this basic principal, it's much more difficult to fit your fingers into the small recesses between the larger items on the board.

Partially populated, all resistors and small parts in place

The battery clips may look crooked, but they were lined up carefully before soldering to ensure a perfect for for a 9V. This is something one doesn't want to try and adjust later as desoldering them can be difficult. The faceplate shown was procured from a DIYAudio group buy. Many thanks to MrSlim and FlynHawaiian for their efforts.

Fully populated board with faceplate

Faceplate from the DIYAudio group buy

There are a number of testing procedures on NwAvGuy's site to ensure the amp is working properly before you plug a pair of headphones in to ensure that you don't inadvertently damage them with high DC output.

A pair of Tenergy 9V rechargables were dropped in and secured with double sided tape and the unit was boxed up with the case specified by the bill of materials, a Box Enclosures B2-080. Gold was chosen as it's a bit more flashy than a plain black box. Screws were replaced with brass counterparts and the knob was a generic aluminum one from the parts bin, possibly made by Kilo.

Assembled Objective 2 amp

Once the amp had a few minutes to burn in, some cans were plugged in for a listen. All online reviews of this amp were avoided so the initial listening could be done without any pre-conceived notions. The amp reminds me quite a bit of the headphone output of the Benchmark DAC from a HeadFi meet. It's very crisp, clear and has strong, effortless bass. The bass may even be a bit better than the Benchmark was, if memory serves correctly. Both amps are quite analytical; I wouldn't choose them for my own personal musical enjoyment as my ears are sensitive and need the treble and upper-midrange to be a bit rolled off or fatigue sets in too quickly. One can see this amp being highly recommended for audio mastering work as it should convey every detail possible to the editor.

Immediately after building the amp, the input and output jacks were shorting with a variety of different plugs. It appears I received a bad batch as I didn't see any other documentation online regarding issues with the Kycon jacks. Rather than replace them with the identical items, Switchcraft jacks will be wired in as they are very trustworthy. The opamps will also be switched to the low-power versions made by Texas Instruments, which hopefully will be a little bit warmer.

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 

JDS Labs CmoyBB v2.03 Headphone Amplifier

The CMoy headphone amplifier came about many years ago as an invention of Chu Moy on the HeadWize headphone board. It was a simple and low-parts design featuring either a single or dual-channel op-amp. There have been many iterations of the CMoy since it was introduced, many of which are put together on a proto-board, and are traditionally stuffed in a Altoids Tin.

A traditionally built CMoy

During a day of wandering the interwebs, I stumbled upon JDSLabs website. JDS has created what he calls the CMoyBB, which is very simply, a CMoy with Bass Boost. In the interest of a simple build, a circuit board was created that fits perfectly within an Altoids tin (including the rounded edges). Depending on one's preferences, a rechargeable version can also be built.

The CMoyBB v2.03 board in beautiful red

There was some notable innovation involved with this design. According to JDS: The cMoyBB v2.03 uses a top-layer ground plane and tightly optimized signal traces, easily outperforming hand-soldered protoboard connections. Proprietary software was used during design of the PCB to check for proper impedance characteristics and negligible crosstalk. Sounds great, where do I sign up? :)

The JDS Labs website has everything you need to get started. The PCB, as well as a number of parts and accessories are carried for your convenience. The documentation is incredibly well laid-out, and includes myriad options should one decide to stray from the standard build. The only thing you need to do is make a quick trip to Mouser with the bill of materials and get the remaining parts. All items below, aside from the Altoids tin and OpAmp socket, were from JDS.

A semi-populated CmoyBB board and Altoids Tin

Between a few parts I had in the parts bin and a Mouser order, the PCB is nearly done. I had a nice 9V battery strap I had procured that's made of hard plastic rather than the typical flimsy PVC you find on some straps. For the film caps, I chose to populate the board with WIMAs, the resistors are nearly all hand-matched carbon film aside from the 10.2K which isn't available, so metal film was used in that position.  As stated ad nauseum in other posts; I prefer carbon film over metal film. The Burr Brown OPA2227PA was chosen for Opamp duty, as I prefer the generally warmer, bassier sound of Burr Brown OpAmps as compared to the general sound of Analog Devices OpAmps. This little board will be configured for single 9V battery operation, so ignore the little yellow capacitor in C5 in the photo below; it won't be needed. 

The fully populated board minus LED

When preparing an Altoids tin (or any other thin tin packaging), delicacy is a must. Either a good quality hole punch should be used, or a hand-drill and Dremel combination with some patience. The latter involves making a very small hole with the drill, then slowly enlarging it with Dremel bits. The hole punch is much easier, but it can be difficult to procure a high-quality one that will punch metal easily. Below is a photo with the 5 holes punched in the tin and some electric tape placed where the PCB will sit. This will prevent any unwanted shorting of the soldered traces on the underside to the tin. 

Punched and prepped Altoids tin

Now the board can be placed inside the prepped tin. Once everything is fit where it is supposed to be, the nuts are screwed to the 1/8" jacks, the knob is placed on the potentiometer shaft, and the plastic grommet for the LED is placed in the corresponding punched hole. The 9V battery is then attached to the battery straps and a piece of adhesive foam placed along the side of the tin. This will prevent the battery from moving about during transport. A small piece of Dynamat was placed underneath to further cushion the battery.

Completed CMoyBB

Here's a photo of the completed amplifier with the case closed. Note that the area above the knob was dremelled away to allow unimpeded volume adjustment. 

Completed CMoyBB - Closed

This was a very quick and enjoyable little project from JDSLabs, and one of the most well thought out CMoy amplifiers I've seen. If you like headphone amplifiers in small candy tins, be sure to check out my post on the Miu Audio RA-1 Amplifier. 

Looking for a custom audio cable for your portable device or amplifier? Zynsonix Audio offers a number of great solutions.  

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 

 

Miu Audio RA-1 Portable Headphone Amplifier

Miu Audio, a recent sponsor on HeadFi.org, offered some freebie kits on their HeadFi sponsor thread a few weeks ago. Of course I was happy to take them up on the generous offer, there are few things more enjoyable than dropping  a few components on a PCB and cranking up the soldering iron.

Miu Audio operates in Shatin, Hong Kong and has been producing gear since 2004. They've created a number of rather interesting looking CD players, as well as an impressive looking little portable tube headphone amplifier, speakers and other audio components.

The Miu Audio iH Tube Headphone Amp

The kit I received was purportedly less exciting than the iH Tube Headphone amp, but still a very capable little machine. The board was noted to be the RA-1 v1.1, which leads me to believe the circuit would be similar to the famous RA-1,  a cute little headphone amplifier housed in mahogany by Brooklyn's Grado Labs.

The Grado Labs RA-1 Headphone Amplifier

Included in the kit was the circuit board and a number of parts in plastic bags, each labelled individually. It may have been nice for the labels to include additional information like capacitor voltage ratings, just in case a potential kit builder wanted to substitute something in the kit without having to track down the schematic and do some math.

The Miu Audio RA-1 v1.1 Circuit Board

Being the compulsive builder than I am, I always measure resistors before dropping them on a board. In rare instances there are mis-marks, slight drifting of vintage carbon comps, or resistors that fall out of their tolerances. I did notice that the resistors in the kit that were supposed to be 100K (100,000) ohms were actually 100 ohms. Simple mistake I'm sure, but it saved me from having to troubleshoot and potential smoke ;) I opted to order some compact Vishay half watt metal film resistors that were a mere 4mm long. They're slightly fatter than the resistors included in the kit, but still fit just fine. I also opted to drop on a gold plated op-amp socket I had in the parts bin rather than the nickel plate included with the kit.

Board with OpAmp socket and resistors fitted

Once these steps were completed, the rest of the components were dropped on piece by piece. This is a very quick build and should be easy to complete in less than an hour.

Completely Populated Board

At the recommendation of another HeadFi member, I replaced the stock op-amp with a Burr Brown 2134AP Op Amp. While the amp isn't the last word in control and detail, it has a pleasing amount of bass and was fun to listen to with my modded and recabled Panasonic RP-HTX7-R1 headphones.

Here is the amplifer dropped into a Godiva Chocolate tin, which seems to be the perfect size!

Completed amp in a Godiva Tin

If you like miniature headphone amps in tins, check out my post on the JDSLabs CmoyBB in an Altoids tin.

Need a custom cable for your portable amp or device? Contact Zynsonix Audio for some great options.

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind.